Device for a Tower for Well Operations and Use of Same

ABSTRACT

A device and method are for well operations. The device includes a tower with an outside and an inside. The tower is provided, on its outside with a work platform vertically movable in the position of use and a vertically movable equipment platform which is independently movable relative to the work platform. The work platform is provided with a hanger device.

The invention relates to a tower provided with vertically movable platforms, the platforms being independently movable. More particularly, the invention relates to a tower for use in well operations in which, in its position of use, the tower is provided with a lower, vertically movable work platform and an upper, vertically movable equipment platform on its outside.

From the petroleum industry it is known to drill holes down through the earth's crust to gain access to the so-called reservoir rocks which contain hydrocarbons in the form of oil and gas. Such holes are known as wells. It is also known to drill so-called injection wells, in which liquid or gas is pumped down to maintain the pressure in the reservoir rocks as the hydrocarbons are extracted. It is also known to pump CO₂ gas down into suitable rocks through injection wells to deposit this greenhouse gas. It is further known to use the same technology, in a sense, to extract water from water deposits located in geological formations. The drilling of such wells is carried out with well-drilling equipment known per se. Further, it is known to use such well-drilling equipment to complete the wells with the necessary casings, tubings and risers.

In subsequent phases of a well's life there is a need for maintenance work to be carried out. The maintenance work may include plugging, perforation of the well casing, installation of sand screens and installation of valves, among other things. For such maintenance work it may be desirable to use lighter equipment than the heavy original drilling equipment, for example a cable (a so-called wire or slick line), a so-called downhole tractor and coiled tubing. The light-weight equipment is quicker to operate and smaller vessels may be used if the maintenance is to be done on a subsea well.

For the desired operations to be carried out, so-called downhole tools are attached to the end of the wireline, downhole tractor or coiled tubing that is lowered first into the well. Among such tools are also tools for fishing up other tools or objects that have either accidentally fallen into the well or got stuck during an operation.

When working in pressurized wells, it is important to prevent so-called blowouts. For this, blowout valves are used. They are known in the art as blowout preventers and will be referred to, in what follows, as BOPs.

It is common to place a BOP at the wellhead, for example on the seabed in the case of an offshore well. In connection with a marine production device fixed to the seabed, a riser runs from the wellhead to the cellar deck. On the riser in the cellar deck is arranged yet another set of valves, the so-called Christmas tree. The Christmas tree is of such arrangement that a wireline, downhole tractor or coiled tubing can be inserted into the riser. This requires that above the Christmas tree, there should be a lock, referred to in the art as a riser, in which the tool is placed first. When the tool is placed within the riser, the riser is first closed at its upper end and then it is opened at its lower end towards the Christmas tree and the pressure within the riser rises to the same pressure as that in the riser. Then the tool may be lowered down the riser and then down the actual well. The riser is formed of a special set of risers, known in the art as riser joints, which are connected into the desired length. For extra safety a special BOP is mounted at the upper end of the riser, through which the wireline or coiled tubing runs. Suitable sealing means are arranged around the wireline or coiled tubing in the form of an adjustable seal, known in the art as a so-called pack box or stripper, for the pressure to be maintained in the riser during the operation. Such means are known within the art and further reference will not be made to them here.

The tool which is lowered into the well to carry out desired operations may typically be 15 metres long. A perforation gun may be 25 to 30 metres long. The use of such a tool will then require the riser to have at least a corresponding length. The riser will therefore project from the Christmas three up through a possible hatch deck and further through a so-called rig-skidding deck. On this deck there is a skid frame, along which the derrick may be moved horizontally. On the rig-skidding deck a special tower may be built around the riser to operate the downhole tool. This tower must be built so high that it projects above the upper end portion of the riser with its BOP and so high that it fixes the equipment which is necessary to drive a wireline or coiled tubing into or out of the well. For a coiled-tubing operation, such equipment may include an injector and, at the top, a so-called goose neck.

The tower built for carrying out light well operations cannot be a permanent one. As mentioned, the riser projects up through the rig-skidding deck and this prevents the drilling rig from being movable along the entire skid frame. The tower is therefore built up from tower modules to the necessary height and dismantled again after use. Building and dismantling of the tower takes time, and during this time, other operations cannot be carried out on the well.

There is a risk that the entire downhole tool or parts thereof may accidentally be dropped or become stuck. The tool must then be fished back up for the well to produce again. For this purpose there are special fishing tools. They may be 10 to 15 metres long. When a fishing tool is used, the riser must be so long that it can hold both the fishing tool and the fished tool. It is therefore common to build the riser so long from the start that it is prepared for this type of accident, even if it will then be considerably longer than what is necessary for the planned well operation. If the riser is not built long enough, it will be necessary, in the event of is an accident downhole, to build the tower higher. This will require more tower modules. If more tower modules are not available, they will have to be provided, with the consequence of further time lost.

Thus, there are several drawbacks to using lighter equipment in order to carry out well operations. It takes time to build the necessary tower on the rig-skidding deck and to dismantle it. The tower is made up of many modules that must be hoisted into place. Crane capacity is a scarce resource on a production platform, and a lifting operation is one of the most hazardous operations performed, with respect to the life and health of the personnel. The tower is modular and is not provided with a lift but with internal stairways. These stairways have to be made so wide that injured personnel may be carried down on a stretcher. This causes the footprint of the tower to be relatively big. The riser is at the centre of the tower. Therefore, the downhole tool must first be hoisted up above the tower and then lowered down through the upper part of the tower until it can be inserted into the upper end of the riser. Operations which include assembling a downhole tool and connecting the complete downhole tool to the wireline or coiled tubing, and also moving the wireline or coiled tubing through the BOP of the riser, are all done at the upper end of the riser. This is cumbersome as the personnel will have to climb a considerable height up the stairs of the tower to get to the work place from the rig-skidding deck.

Patent document WO 2009/001088 discloses a tower on board a vessel arranged for the drilling of subsea wells and operations in such wells. To carry out coiled-tubing operations, the tower is provided with a frame, there being arranged within the frame a first fixed upper platform holding an injector, an adjustable seal and a goose neck, and a second fixed lower platform holding a BOP. When the coiled-tubing equipment is not in use, or when it is being prepared, the frame is parked outside the tower. Prior to operation the frame is moved sideways into the tower by means of guiding arms and possibly a crane, so that the frame hangs from the crown block of the tower above the centre well, the so-called moon pool, of the vessel. The lifting of tools for assembly is carried out by the cranes of the ship.

Patent document GB 2399838 discloses a foldable tower for use in coiled-tubing operations, especially on board a vessel, a floating drilling platform or a tension-leg platform. In its position of use, the tower consists of a frame with two or more vertical frame elements or legs. The purpose of the frame is to transfer the weight of a lower BOP and upper coiled-tubing equipment from the wellhead to the vessel or to the drilling platform. Between the legs of the frame is placed a lower platform for the BOP. This platform can move vertically relative to the frame. Between the legs of the frame is further placed an upper platform for the upper coiled-tubing equipment which includes, inter alia, an injector and a goose neck. This platform can move vertically independently of the BOP platform. The injector can be moved horizontally away from the longitudinal axis of the riser or in towards it. The riser is between the legs of the frame and thus within the frame. The frame is further provided with means for heave compensation. Downhole equipment to be placed in the riser is hoisted in by an external crane. The upper transverse element of the frame provides a height restriction for the length of downhole equipment that may be hoisted into the frame.

Patent document US 2004/0206551 shows a drilling rig in the form of a mast mounted on a trailer. A platform for a coiled-tubing injector is fixed to one side of the mast and the coiled-tubing injector rests on the platform. The mast is raised by a pivoting arrangement at the lower end of the mast and the pivoting arrangement is fixed to the fixed rotary table of the rig. A BOP hangs underneath the fixed rotary table.

Patent document U.S. Pat. No. 6,032,744 discloses a drilling rig in which an injector for coiled-tubing operations, among other things, is hangingly mounted underneath a work platform and in which there is a fixed distance between a BOP located below the injector and the injector. A goose neck for guiding the coiled-tubing down into the injector is above the work platform. The injector and the goose neck are therefore separate components. In one embodiment, the goose neck can be moved vertically along a mast while the injector is stationary. In an alternative embodiment, a reel for the coiled tubing is mounted for vertical movement in said mast.

Patent document U.S. Pat. No. 6,431,286 shows a drilling rig provided with a derrick in the form of a bipartite mast mounted on a trailer. A cradle, which is arranged to fix a coiled-tubing injector on its bottom side, is movable along the sides of the mast facing each other, and in such a way that the coiled-tubing injector is moved along the outer sides of the mast. The derrick is arranged to hold a BOP.

In addition to the well operation methods mentioned, a method known in the art as snubbing is also used. Snubbing means that a pipe string consisting of threaded pipe sections is moved into a pressurized well through a BOP. A jack is used to force the pipe down the well to overcome the well pressure.

By downhole equipment is meant, here, equipment which is placed in a well and left there. By a downhole tool is meant, here, a tool which is moved out of the well again after having performed its task.

The invention has for its object to remedy or reduce at least one of the drawbacks of the prior art, or at least provide a useful alternative to the prior art.

The object is achieved through features which are specified in the description below and in the claims that follow.

In a first aspect the invention relates to a device for well operations including a tower with an outside and an inside, the tower being provided, on its outside, with a work platform vertically movable in the position of use and a vertically movable equipment platform which is independently movable relative to the work platform, and the work platform being provided with a hanger device. This has the advantage of there being free access to the centre of the well for hoisting downhole equipment and downhole tools into the well, and of the lift not needing to be higher than for it to freely pass the equipment platform when this is in a low position. This has further the advantage of enabling the connecting of downhole equipment, downhole tools and for example coiled tubing, wireline or a snubbing string to be done from the work platform. Thereby, working high up in the tower is avoided, and personnel do not have to walk up and down great heights on a stairway, which increases the efficiency of the operation. The fact that the work platform is provided with a hanger device has the advantage of the work platform temporarily holding the weight of the riser while it is being assembled or disassembled, and while equipment or a tool is being placed in the riser. This has further the advantage of the work platform being usable for lifting or lowering the riser relative to the Christmas tree. The hanger device may include a so-called false rotary and wedge belts. The wedge belts are also called slips. In an alternative embodiment the hanger device may include a gripper claw of a kind known per se.

At least one of the work platform and the equipment platform may be provided with attachment means for movable attachment to the outside of the tower. Such attachment means are well known within the art and may include a guide carriage, a so-called dolly, and an associated dolly guide in the form of a rail. The work platform and the equipment platform can be lifted and lowered in a manner known per se, by the use of, for example, a pitch rack, hydraulic pistons, a winch or sheaves. Necessary motors can be electrically driven or hydraulically driven.

The work platform may be provided with a BOP. The equipment platform may be provided with at least one piece of well operation equipment selected from the group consisting of an injector, wireline operation equipment and snubbing equipment. This has the advantage of the device being usable for several types of well operations.

In its position of use, the injector may be provided with means for horizontal and vertical movement relative to the equipment platform.

The tower may be arranged to receive a magazine for well equipment such as riser joints, for example. The magazine may be provided with an opening facing the work platform and the equipment platform. In one embodiment the equipment platform may be provided with a pick-up mechanism for manipulating well equipment. This has the advantage of the magazine containing the necessary components and sections for building the riser and these being in a vertical position. The cooperation of the magazine, the vertically movable equipment platform and the pick-up mechanism of the equipment platform, reduces the number of necessary crane lifts, and the assembly will be quicker as the components and sections of the riser may be moved a short, horizontal distance. This has further the advantage of an extra riser joint being ready in the magazine in case there is a need to extend the riser by an accident, it being necessary, for example, to fish up damaged equipment or damaged tools from the well. As the equipment platform can be moved higher up in the tower, there is room for the extra riser joint between the BOP and the equipment platform without the tower having to be extended. Such an extension of the riser can be done quickly, while at the same time, there is time saved by not mounting this last riser joint during the ordinary assembling of the riser as there will only exceptionally be a need for such a long riser.

In one embodiment, the tower may be provided with an external, vertically positionable manipulator arm. Because of the external position of the work platform and equipment platform, and the fact that they are vertically movable, an external manipulator arm may get sufficiently high up to swing downhole equipment and downhole tools in above the BOP. This has the advantage of enabling the number of lifts by an external crane to be reduced.

In a further embodiment, the tower may be provided with a vertically positionable lift. In yet another embodiment, the tower may be arranged to be transported in a horizontal position and provided with means in the form of, for example, a lug for vertical positioning at a point of use. This has the advantage of the tower being portable as one unit, thereby avoiding work and time for building a modular tower.

In a second aspect, the invention relates to a method for well operations including the use of a tower with an outside and an inside, the tower being provided, on its outside, with a work platform vertically movable in the position of use and a vertically movable equipment platform which is independently movable relative to the work platform, and the work platform being provided with a hanger device, the hanger device being temporarily brought to hold a riser or a riser joint fixed.

The method may further include the steps of:

-   -   picking up a riser joint from the magazine in the tower by means         of a pick-up mechanism with which the equipment platform is         provided;     -   moving a first riser joint, by means of the pick-up mechanism of         the equipment platform, above the centre of a hanger device with         which the work platform is provided;     -   lowering the equipment platform until the hanger device can be         brought to engage and be brought to hold the riser joint fixed         at its upper end portion;     -   bringing the pick-up mechanism to disengage from the riser joint         and lowering the equipment platform to pick up a second riser         joint from the magazine;     -   carrying the second riser joint above and in the extension of         the first riser joint, subsequently lowering the equipment         platform until the second riser joint meets the first riser         joint and the two riser joints are connected;     -   bringing the hanger device to release its grip on the first         riser joint;     -   lowering the equipment platform together with the riser until         the hanger device can grip the upper end portion of the second         riser joint;     -   repeating the operation until the riser is completed;     -   bringing the equipment platform to lift a BOP to the top of the         riser for the BOP to be attached to the riser; and     -   bringing the equipment of the equipment platform, selected from         the group consisting of an injector, wireline operation         equipment and snubbing equipment, to fit against the BOP in a         sealing manner.

The method may further include the steps of:

-   -   parking the injector on the equipment platform to one side of         the centre of the BOP; and     -   preparing the injector by threading coiled tubing through the         injector.

The method may further include the steps of:

-   -   bringing a vertically movable manipulator arm on the outside of         the tower to move to pick up a piece of downhole equipment or a         downhole tool which is on a deck on which the tower stands;     -   carrying the manipulator arm so high up along one of the guide         rails of the tower that the downhole equipment or the downhole         tool can be swung in above the centre of the BOP and then be         lowered into the riser;     -   hanging the downhole equipment or downhole tool off on a         C-plate;     -   disengaging the manipulator arm from the downhole equipment or         downhole tool;     -   repeating the method and joining the downhole equipment or         downhole tool into a downhole assembly;     -   attaching the downhole assembly to coiled tubing or a wireline.

The method may further include the step of:

-   -   carrying the injector or cable operation equipment above the         centre of the BOP and connecting the injector or the wireline         operation equipment to the BOP in a sealing manner.

The method may further include the step of:

-   -   connecting the riser containing the downhole assembly to a         Christmas tree in a sealing manner.

The method as described above may be carried out in the re-verse order.

In what follows is described an example of a preferred embodiment which is visualized in the accompanying drawings, in which:

FIG. 1 shows a side view of a tower, when in the position of use, having a lower, vertically movable work platform and an upper, vertically movable equipment platform, the work platform being in its lower position; and

FIG. 2 shows a view of the tower and platforms as shown in FIG. 1, viewed from above.

In the figures, the reference numeral 1 indicates a device in accordance with the invention. In FIG. 1 a tower 2 is provided, on its outside 22, with an, in the position of use, lower, vertically movable work platform 3 and an upper, vertically movable equipment platform 4. On its one outside 22, the tower 2 is provided with two vertical guide rails 24. On a side facing the tower 2, the work platform 3 is provided with at least one dolly 32 which is of a kind known per se, and will not be mentioned in further detail. In the figures are shown two dollies 32, each moving along a respective vertical guide rail 24. On a side facing the tower 2, the equipment platform 4 is provided with at least one dolly 42 of a kind known per se. In the figures are shown two dollies 42, each moving along a respective vertical guide rail 24.

On its inside 25, the tower 2 is provided with fixed tower decks 26 and ladders 28 for internal access to the different height levels of the tower 2 and for evacuation of the tower.

In the example the equipment platform 4 is provided with an injector 5 of a kind known per se, arranged to move coiled tubing (not shown) into and out of a well (not shown). The injector 5 is provided with a fixed goose neck 52 of a kind known per se. The injector 5 and the goose neck 52 will not be described in detail. The injector 5 stands by way of four height-adjustment mechanisms 54 on an injector base 56 which is movably attached to the equipment platform 4. The injector base 56 is horizontally movable in a direction indicated by an arrow in the drawings and horizontally movable in a direction perpendicular to the indicated direction. Underneath the injector 5, the injector 5 is provided with an adjustable seal 58 which may be a so-called stripper or a pack box, and a hydraulic quick-release coupling 59 for attachment to a riser joint or a BOP 34.

In the example the work platform 3 is provided with a BOP 34 which is of a kind known per se and will not be mentioned in any further detail. The work platform 3 is further provided with an opening (not shown) for a riser to be passed through vertically, and the work platform is further provided with a hanger device 36 which may be a so-called false rotary with wedge belts, referred to as slips within the art.

FIG. 2 shows the tower 2 with the equipment platform 4 viewed from above, most of the work platform 3 being hidden. The FIG. 2 is simplified and some details have been omitted. Between the guide rails 24, the tower 4 is arranged to receive a magazine (not shown) for well equipment, such as components for building a riser (not shown). The magazine is placed in the open space 27 between the guide rails 24. The magazine may be a fingerboard or be arranged to be rotatable. A pick-up mechanism 7 of a kind known per se is arranged to pick up well equipment from the magazine. In this example, the pick-up mechanism 7 is movably attached to the injector base 56. In its position of use, the pick-up mechanism 7 may move horizontally in the same direction as the injector base 56, indicated by an arrow, and horizontally in a direction perpendicular to the moving direction of the injector base 56.

On its outside 22, the tower 2 is provided with a vertically movable manipulator arm of a kind known per se (not shown). The manipulator arm is attached to one of the guide rails 24 of the tower and is arranged, in a manner known per se, to move vertically along the guide rail 24. With a gripping device of a kind known per se, the manipulator arm is arranged to pick up a downhole tool or downhole equipment from the deck (not shown) on which the tower 2 stands, lift it up and carry it in above the centre of the riser and the BOP 34 in order then to lower the tool through the BOP 34 into the riser. Correspondingly, in the reverse order, the manipulator arm can carry a downhole tool out of the riser and place it on the deck on which the tower 2 stands. On its outside 22, the tower 2 is further provided with a vertically movable lift of a kind known per se (not shown). The lift is attached to one of the guide rails 24 of the tower and moves vertically along it. The manipulator arm and lift are attached to separate guide rails 24. The lift is arranged to be able to stop at the internal platforms 26 of the tower 2, at the work platform 3, no matter what height level the work platform 3 is at, and at the equipment platform 4, no matter what height level the equipment platform 4 is at.

On the outside 22, at its one end portion 29, the tower 2 is provided with a lug 8 on two of the outsides 22 of the tower 2. The tower 2 can be transported in a horizontal position on is board a supply ship, for example, and hoisted in its horizontal position over to its point of use. At the tower's 2 point of use is arranged a raising mechanism (not shown) which grips the lugs 8 and raises the tower 2 into a vertical position of use. The magazine with well equipment can be placed between the guide rails 24 of the tower 2 before the tower 2 is raised. After the tower 2 has been raised, the work platform 3 and the equipment platform 4 are hoisted into place, and they are attached via their dollies 32, 42 to the guide rails 24. The manipulator arm and the lift are also hoisted into place and attached to their respective guide rails 24.

In what follows is explained how the invention is used in a coiled-tubing operation. The skilled person will know how a corresponding operation can be performed by the use of a cable, wireline tractor and snubbing, and also what equipment will have to be placed on the work platform and equipment platform for such operations.

The work platform 3 is adjusted to the desired level. The equipment platform is provided with the injector 5 and the pick-up mechanism 7. The equipment platform 3 is lifted to the correct height in order to pick up, by means of the pick-up mechanism 7, the first riser joint in the magazine between the guide rails 24 of the tower 2. The work platform 3 is provided with a hanger mechanism 36 in the form of a so-called false rotary and slips. The injector base 56 and the pick-up mechanism 7 move the riser joint to the centre of the hanger device 36. The equipment platform 4 is lowered to the desired level. The hanger device 36 is brought to engage with the riser joint at the upper end portion thereof and holds the riser joint fixed. The pick-up mechanism 7 is disengaged from the riser joint and the equipment platform 4 is lifted to the correct height in order to pick up the second riser joint from the magazine by means of the pick-up mechanism 7. The second riser joint is carried above and in the extension of the first riser joint. Then the equipment platform 4 is lowered until the second riser joint meets the first riser joint and the two riser joints are connected. Then the grip of the hanger device 36 on the first riser joint is released and the equipment platform 4 is lowered together with the riser until the hanger device 36 can grip the upper end portion of the second riser joint. A branch pipe of a type known per se is placed on top of the upper end portion of the second riser joint by means of the manipulator arm or by lifting and lowering the equipment platform 4. The branch pipe serves as a circulation port for a return fluid flow from the well. Then a third riser joint is placed on top of the branch pipe in the same way as described for the first and second riser joints. Finally, by means of the hydraulic quick-release coupling 59 of the injector 5, the equipment platform 4 lifts the BOP 34, which has been parked on the work platform 3, into place over the riser joint fitted last.

The injector 5 is moved aside and parked, so that it will not be in the way of downhole equipment or a downhole tool which is to be lowered into the riser. The coiled tubing (not shown) is passed through the injector 5 in a way known per se and further reference will not be made to it here.

The manipulator arm is then run down to the deck and picks up the desired downhole equipment or downhole tool. Then the manipulator arm is run so high up that the downhole equipment or downhole tool may freely be turned in above the centre of the BOP 34 and then lowered into the riser. The downhole equipment or downhole tool is hung off on a so-called C-plate. Then the manipulator arm is disengaged from the down-hole equipment or downhole tool and returns to pick up the next piece of downhole equipment or downhole tool. The downhole equipment or downhole tool is joined together by personnel present at the BOP 34. When the downhole equipment and/or downhole tool have/has been assembled into a so-called downhole assembly, known in the art as a bottom-hole assembly, the bottom-hole assembly is connected to the coiled tubing. The injector 5 is moved above the BOP 34 and connected to the BOP with the hydraulic quick-release coupling 59. The coiled-tubing arrangement is now ready for use. Connecting and disconnecting the lower portion of the riser to/from the Christmas tree is done in a known manner and is not described here.

In an alternative embodiment, the work platform 3 is provided with a hanger mechanism 36 in the form of a gripper claw of a type known per se (not shown).

In an alternative embodiment, the point of use of the device 1 is made up of a movable bridge, not shown, provided with a bridge deck. Further, on its underside, the bridge is provided with two bridge pillars projecting downwards. The downwards-projecting bridge pillars may be constituted by a metal structure. At their lower ends, the bridge pillars are provided with means arranged to skid on a first skid frame on a rig-skidding deck. In a preferred embodiment, the longitudinal direction of the bridge is perpendicular to the skid frame on the rig-skidding deck. The bridge deck is provided with a second skid frame extending in the longitudinal direction of the bridge. The device 1 is provided with means (not shown) arranged to skid on the second skid frame. By moving the device 1 along the second skid frame of the bridge and by skidding the bridge along the first skid frame of the rig-skidding deck, the device 1 can be carried to a selected position on the rig-skidding deck. Between the second skid frame the bridge deck is provided with hatches where the riser can be moved down from the device 1 to and through hatch openings in the rig-skidding deck and down to the Christmas tree on the cellar deck.

The device 1 is used to assemble a riser as earlier described above a first Christmas tree on the cellar deck. After the work has been carried out in the first well, the bottom-hole assembly is removed from the riser, if necessary. The lower end of the riser is disengaged from the Christmas tree. The hanger device 36 of the work platform 3 holds the riser fixed. By lifting the work platform 3, the lower end of the riser is hoisted from the cellar deck, and this in such a way that the lower end of the riser projects above the rig-skidding deck when the work platform 3 has been moved upwards to an upper portion of the tower 2. Thereby is achieved that the device 1 can be moved into a position above another well by skidding the tower 2 along the skid frame of the bridge and by skidding the bridge along the skid frame of the rig-skidding deck without the riser having to be separated. When the device has arrived at a new, desired position, the riser is lowered by lowering the work platform 3 until the lower end of the riser can be connected to a second Christmas tree on the cellar deck. The equipment platform 4 is moved in such a way that it will not get in the way of the work platform 3. In this embodiment, considerable time is saved when there is work to be carried out in several wells.

In an alternative embodiment the riser is not disengaged from the hydraulic quick-release coupling 59. After the lower end of the riser has been disengaged from the Christmas tree and the riser has possibly been disengaged from the hanger device 36 of the work platform, the riser can be lifted and lowered by means of the equipment platform 4. In this embodiment too, considerable time is saved when there is work to be carried out in several wells.

In a further alternative embodiment, lifting and lowering the riser can be carried out by the riser being held simultaneously by the hanger device 36 of the work platform 3 and by the hydraulic quick-release coupling 59, and by the work platform 3 and the equipment platform 4 cooperating by being lifted or lowered at the same speed. This has the further advantage of the riser being held fixed by two independent mechanisms, which increases the safety of the operation. 

1. A device for well operations comprises a tower with an outside and an inside, the tower being provided, on its outside, with a work platform vertically movable in the position of use and a vertically movable equipment platform which is independently movable relative to the work platform, wherein the work platform is provided with a hanger device.
 2. The device in accordance with claim 1, wherein the hanger device includes a false rotary and slips.
 3. The device in accordance with claim 1, wherein the hanger device includes a gripper claw.
 4. The device in accordance with claim 1, wherein the work platform is provided with a blowout preventer.
 5. The device in accordance with claim 1, wherein the equipment platform is provided with at least one piece of well operation equipment selected from a group consisting of an injector, cable operation equipment and snubbing equipment.
 6. The device in accordance with claim 5, wherein, in its position of use, the injector is provided with means for horizontal and vertical movement relative to the equipment platform.
 7. The device in accordance with claim 1, wherein the tower is arranged to receive a magazine for well equipment.
 8. The device in accordance with claim 7, wherein the magazine is provided with an opening facing the work platform and the equipment platform.
 9. The device in accordance with claim 1, wherein the equipment platform is provided with a pick-up mechanism for manipulating the well equipment.
 10. The device in accordance with claim 1, wherein on its outside the tower is provided with an external, vertically positionable manipulator arm.
 11. The device in accordance with claim 1, wherein on its outside the tower is provided with a vertically positionable lift.
 12. The device in accordance with claim 1, wherein the tower is arranged to be transported in a horizontal position and provided with means for vertical positioning at a point of use.
 13. A method for well operations including the use of a tower with an outside and an inside, the tower being provided, on its outside, with a work platform vertically movable in the position of use and a vertically movable equipment platform which is independently movable relative to the work platform, the method comprising providing the work platform with a hanger device and temporarily bringing the hanger device to hold a riser or a riser joint fixed. 